1. Field of the Invention
The present invention relates to a color filter for use in a color liquid crystal display device and to a liquid crystal display device provided with the color filter.
2. Description of the Related Art
A color liquid crystal display device is essentially constituted by a first transparent substrate having a first transparent electrode layer formed thereon, a second transparent substrate having a second transparent electrode layer formed thereon, and a liquid crystal layer sealed between these transparent substrates. A color filter is generally interposed between the second transparent substrate and the second transparent electrode layer. The color filter includes a black matrix as a light-shielding pattern and fine stripe filter segments of red, green and blue arranged in parallel to or intersected with each other on the surface of a transparent substrate such as glass, or fine filter segments horizontally and vertically arranged at a constant sequence.
On the outer sides of the first and second transparent substrates, there are arranged a first polarizer and a second polarizer, respectively. Further, on the outer side of the first polarizer, there is arranged a backlight unit including a backlight source.
With such a liquid crystal display device, the display of images is performed in such a manner that the voltage applied across the first and second transparent electrode layers is adjusted individually for each filter segment, and the magnitude of polarization of the light from the backlight unit passed through the first polarizer is controlled to thereby control the light amount passing through the second polarizer. Therefore, the chromatic characteristics of the color filter and of the polarizer are both important factors which determine the chromatic characteristics of liquid crystal display device.
In recent years, various advantageous aspects of the liquid crystal display device such as space-saving, weight-saving and power-saving due to its thin flatness are increasingly favorably evaluated, so that the application of liquid crystal display device is now rapidly expanded to televisions as well as to monitors of a large size. Thus, it is now increasingly desired for the color filter, which determines the chromatic characteristics of liquid crystal display devices, to have enhanced luminance, color reproduction and contrast.
However, the conventional color filters are different in chromaticities of the parallel-transmitted light passing through the color filter (the light transmitted through two polarizer sandwiching the color filter, with the axes of polarization of the polarizers being made parallel with each other) and the orthogonal-transmitted light passing through the color filter (the transmitted light slightly leaking through two polarizer sandwiching the color filter, with the axes of polarization of the polarizers being orthogonally intersected with each other). Therefore, the chromatic characteristics at the white image-displaying time in the liquid crystal display device become different from the chromatic characteristics at the black image-displaying time, often resulting in display of somewhat tinted images at the black image-displaying time, thus deteriorating the visibility of images. As a result, it has been difficult to obtain a television or monitor of a large size having satisfactory display qualities.
In order to solve these problems, it has been proposed for a ratio between a maximum contrast ratio (CR1) of color pattern and a minimum contrast ratio (CR2) of color pattern among the color patterns of each color to satisfy the relationship of: CR1/CR2≦1.6 (see Jpn. Pat. Appln. KOKAI Publication No. 2001-194658). This proposal is intended to restrict the contrast ratio of each of color filter segments to a predetermined range, thereby making the quantity of light leakage amount uniform at the black image-displaying time, thus minimizing the tinting of black images.
Further, the chromatic characteristics of the polarizer itself which influences the chromatic characteristics of liquid crystal display devices also differ where the axes of polarization are made parallel with each other or where the axes of polarization are orthogonally intersected with each other. Where the axes of polarization are orthogonally intersected with each other, images visible on the display would be much more tinted with blue color as compared with where the axes of polarization are made parallel with each other. Therefore, it has been proposed to adjust not only the chromaticity of parallel-transmitted light but also the chromaticity of orthogonal-transmitted light to a predetermined range (see Jpn. Pat. Appln. KOKAI Publication No. 2002-214436).
Many of the conventional liquid crystal display devices display bluish images at the black image-displaying time due to the influence by the polarizers. Therefore, even if the contrast ratio of each color filter segments of the color filter is made uniform, it is impossible to prevent visible images from becoming considerably bluish at the black image-displaying time, thus still failing to completely solve the problem that a difference in chromatic characteristics is caused to occur at the white image-displaying time and at the black image-displaying time.